1. Field of the Invention
The present invention relates to a method for recovering indium from an indium-containing material.
2. Description of the Related Art
As a conductive compound of the III-V group, indium is utilized in intermetallic compounds such as InP, InAs, and the like, in indium oxide doped with tin (ITO) as a material for use in solar cells, and in transparent conductive thin films. It is expected that the demand for indium will become increasingly greater in the future.
Conventionally, there has been no principal ore for indium; industrially, indium has been produced by recovering indium as a by-product in zinc purification or lead purification, e.g., by recovering indium concentrated in soot and smoke. Accordingly, raw materials used for the recovery of indium contain large amounts of metal impurities such as Zn, Fe, Cu, Al, Ga, As, Cd, and the like. Furthermore, many types of components other than these metal components are also contained in trace amounts.
Accordingly, a complicated process is required in order to remove these metal impurities and recover high-purity indium. Generally, the abovementioned indium recovery process is accomplished by a combination of electrolytic purification methods and chemical purification such as (A) methods in which indium is precipitated as a hydroxide by adjusting the pH, (B) methods in which indium is precipitated as a sulfide by adding a sulfurizing agent, (C) methods in which indium is substituted and deposited by adding metals such as Al, Zn, Cd, Zn—Cd alloys, and the like, (D) methods in which indium is recovered by solvent extraction, (E) methods in which indium is recovered by an ion exchange method, and the like.
However, in the abovementioned recovery processes, methods according to (A) are methods which utilize differences in the pH regions where metal ions produce hydroxides. For example, a method in which Zn and Al are dissolved and In is precipitated and recovered as a hydroxide by raising the pH to 12 or greater is used as a method for separating In from Zn and Al. In this method, however, the In hydroxide that is produced has extremely poor filtration characteristics; accordingly, the size of the filtration equipment is increased, and the operation also requires a long time. In this method, it is also difficult to separate In from impurities such as Fe, Cu, As, Cd, and the like.
The methods of (B) utilize differences in the solubility product of metal sulfides: in such methods, low-purity sulfides containing various metal impurities such as those described above are produced in large quantities. These sulfides generally have poor filtration characteristics; furthermore, in cases where the In sulfide obtained is extracted, it is difficult to extract the In completely using sulfuric acid alone. Accordingly, such methods suffer from the problem of being difficult to apply to wet zinc processes.
A problem is involved in (C) such that in cases where impurities that are nobler than In are contained, separation of In from these metals is impossible.
A problem is involved in (D) and (E) such that a burden is placed on the pre-processing by the impurities that are separated from In; furthermore, the running cost is high.
In all of the chemical purification methods described above, the separation of impurity metals is inadequate. Accordingly, neither can a simple electrowinning method (in which the object metal is extracted into an aqueous solution, electrolysis is performed using an insoluble anode, and a high-purity metal is obtained in a single process at the cathode) be used as a combination electrolytic purification method, and it has been unavoidably necessary to use a cumbersome electrolytic purification method (in which crude metal is used as the anode, and purification is performed by electrolysis of the high-purity metal at the cathode).
Accordingly, each of the methods described above has a respective problem. Combinations of the abovementioned methods are used for actual recovery, and the process used in order to recover high-purity In become complicated and bothersome; this has not been an economical method.
In Patent Document 1, the present inventors proposed a method for recovering indium from an indium-containing material including an acid extraction step in which the indium-containing material is subjected to extraction processing with an acid, and metals that are soluble in the acid are dissolved together with In; a step of removing Cu and the like in which a sulfurizing agent is added to the extract obtained in the abovementioned acid extraction step while adjusting the oxidation-reduction potential, and metals other than In such as Cu and the like are removed by precipitation; a sulfurizing and precipitation step in which sulfuric acid and a sulfurizing agent are added to the aqueous solution of indium obtained in the abovementioned step of removing Cu and the like, and In is precipitated and concentrated as a sulfide; an SO2 extraction step in which In is selectively extracted by blowing SO2 gas into the indium sulfide obtained in the abovementioned sulfurizing and precipitation step in the presence of sulfuric acid acidity; a substitution deposition step in which the pH and solute SO2 concentration of the indium-containing extract obtained in the above-mentioned SO2 extraction step is adjusted, a metal powder is then added, and an indium sponge is deposited by substitution; a hydrochloric acid extraction step in which the indium sponge obtained in the abovementioned substitution deposition step is extracted with hydrochloric acid; a step of removing Cd and the like in which a sulfurizing agent is added to the indium extract obtained in the abovementioned hydrochloric acid extraction step, residual metal ions of Cd and the like are removed by precipitation, and a starting electrolytic solution is obtained; and an electrowinning step in which the starting electrolytic solution obtained in the abovementioned step of removing Cd and the like is electrolyzed, and high-purity metallic indium is obtained.
[Patent Document 1] Japanese Laid-Open Patent Application No. 11-269570.